SESCI 2005 Conference British Columbia Institute of Technology, Burnaby, British Columbia, Canada August 20 - 24, 2005 ADVANCED THERMAL SOLAR SYSTEM WITH HEAT STORAGE FOR RESIDENTIAL HOUSE SPACE HEATING By Kazimierz Szymocha Alberta Research Council Inc., 250 Karl Clark Road, Edmonton, Alberta, Canada T6N 1E4 Phone: 780-450-5466, Fax: 780-450-5477, E-mail: [email protected], Website: http://www.arc.ab.ca ABSTRACT Increasing energy consumption, shrinking resources and rising energy costs will have significant impact on our standard of living for future generations. In this situation, the development of alternative, cost effective sources of energy for residential housing has to be a priority. Designing energy efficient and affordable dwellings located in harsh climate regions like Canada, present significant challenges. This paper presents the advanced technology and some of the unique features of a novel solar system that utilizes solar energy for space heating in residential housing and commercial buildings. The improvements in solar technology and integration of the solar system with the house envelope offers a significant cost reduction, to a level where the solar system can compete with the energy costs from existing sources. In the year 2000, the Alberta Research Council Inc. (ARC) started to work on the development of thermal solar systems that were designed for application in residential housing for the purpose of space heating. As a result of this research activity, a cost effective thermal solar collector with direct heat storage (DHS) was developed and tested. During the last year, the prototype DHS solar system was installed on experimental shelter and extensively tested through the 2004-05 winter season. ARC has conceived and proven a new concept that can collect solar energy and store the heat during the day and release the heat during the night. Conducted field tests in the winter season has demonstrated that DHS solar thermal panels can reduce space heating energy consumption by about 50% compared to traditional residential housing construction technology. This paper delivers a description of the new solar technology and presents results of tests and performance evaluation. Results of testing prove that this new technology could be implemented in a cost-competitive, environmentally responsible and sustainable manner. 1 INTRODUCTION The peaking of the North American natural gas production in 2003 (ERA, 2004) presents a serious problem. North American natural gas reserves estimates now appear to have been excessively optimistic and North America natural gas production is now in decline (Hirsh, 2005). North America is moving to a period in its history in which it will no longer be self-reliant in meeting its growing natural gas needs. In Alberta, the production of natural gas achieved a peak in the year 2001. It is estimated that the remaining established natural gas reserves left in Alberta are sufficient for the next eight and half years only (AUB, 2004). In Canada, natural gas is the basic fuel used for heating in residential housing and commercial buildings. It is a time to stop wasting valuable and scarce resources of natural gas to produce heat that can be easily and cheaply provided by thermal solar systems. Under existing circumstances the development of alternative, cost effective sources of energy for residential housing has to be a priority In Europe 40% of energy is consumed in buildings, more than by industry or transport. All over Europe a number of solar heat generation systems are on the rise. In Germany, which is the leading country, in 2004 the growth of the newly installed thermal collectors was about 750,000 m2 with a total capacity of 525 MW (Stryi-Hipp, 2005). Solar thermal systems are installed on almost 20% of single family houses in Austria (Piria, 2005). However, in general the solar thermal systems market still remains in Europe at a very early stage of development. Globally, installed solar thermal systems capacity in 2004 was about 69 GW and presents one of the most important renewable energy sources worldwide. The European Commission has presented its program and goals with respect to future development of renewable energy sources in the White Paper (Aitken, 1997). The strategic goal of the White Paper is to increase the market share of renewable sources of energy to 12% by the year 2010. In 2005 in Europe, to promote the thermal solar systems technology, a European Solar Thermal Platform was created. In Europe almost 50% of final energy consumption is used for heating purposes. In Canada, energy usage by residential and commercial buildings accounts for about 30% of the total consumed energy (Ayoub, 2000). Of the total energy consumption for an average Canadian house, 65% of energy is used for space heating, 20% for hot water generation and 15% in form of electricity. Hence, reducing energy usage for space heating, which takes the largest portion of energy, can make the greatest contribution to decrease the total energy consumption of Canadian houses. Table 1 shows the energy demand for a typical residential house in Canada and in Europe. Table 1. Energy Consumption by Average Canadian and European Residential House Energy usage Canadian House* European House Space heating 65% 57% Hot water generation 20% 25% Electricity 15% 18% * Average Canadian house consumes per year 150 GJ of heat and 26 GJ (7,200 kWh) of electricity (NRCan, 2002) In the past, the thermal solar market was dominated by domestic hot water systems, but recent years show the emergence of a new solar thermal system called a combi system. The combi solar system brings together the hot water generation and the space heating in one system. A typical hot water system size is about 5 m2 whereas a combi system size ranges from 12 to 25 m2. The first industrial production lines for solar thermal collectors have just recently been completed, signaling the beginning of the solar industrialization era (Wittwer, 2005). 2 Besides hot water and space heating applications, process heat with a 200ºC temperature range, is a very interesting area for application. Large scale utilization of solar thermal energy systems is closely related with the availability of low-cost, effective heat storage systems. For effective heat storage a new system that applies phase change materials is under development. As outlined earlier, existing natural gas proven deposits, at the current rate of production, are sufficient only for the next eight years. As a result a serious shortage of natural gas in the near future can be expected. Progress in solar modules technology and integration of the solar systems with improved house envelope offer, a significant renewable energy cost decrease to the level where the solar system can compete with the cost of energy from traditional sources of energy. SOLAR COLLECTOR DESCRIPTION In 2002, at ARC's lab, the first solar thermal collector with the ability for direct heat storage (DHS) was developed. A phase change material (PCM) with a melting/solidification temperature of 29ºC was used for heat storage. When the PCM undergoes the phase change, it can absorb or release a large amount of energy (~190 kJ/kg) as latent heat. The phase change material was introduced into the DHS collector in the form of a matt with PCM enclosed in the capsules. The DHS solar system generates and store on-site thermal energy for the purpose of space heating. During the daytime the wall installed DHS solar collector is charged by the sun and accumulates heat for the night. The thermal solar collector with direct heat storage (DHS) consists of a thin solar radiation absorption layer combined with a PCM matt that is covered with a transparent cover as shown in Figure1. During the day, when the panel is exposed to the sun, the collector absorbs the solar radiation, generates heat and uses it for phase change material melting. During the night, the melted PCM solidifies and delivers heat that keeps the panel warm for a prolonged period of time, practically most of the night. The purpose of the DHS panel is to keep the outside wall temperature warm (over 20ºC), to prevent heat loss through the wall. There is negligible heat transfer and heat loss if the differential temperature is close to zero. The DHS thermal solar collector is designed to be integrated with a house envelope and accumulate the thermal energy directly into the wall of the dwelling. The ARC manufactured DHS solar panel is shown in Figure 1b. In 2003, the prototype DHS collector was assembled as a stand alone movable module and tested over the winter period. Using a set of temperature sensors arranged inside the DHS panel, data on temperature distribution was collected and evaluated. A series of tests were performed at different levels of the solar irradiation and at different ambient temperatures. To perform an evaluation of the DHS system, two reference surfaces (black painted metal plate and standard vinyl siding) were also introduced into the testing system. An example of the results for the prototype DHS collector and reference walls is shown in Figure 2. As can be seen, the temperature of the wall equipped with a DHS panel even on a short, semi-cloudy winter day can be kept at over 20ºC through most of the night (until 7 am of the next day). The results proved to be very positive from the perspective of the system’s performance and thus validated further development the DHS solar system concept. A solar collector with a direct heat storage system that utilizes